Fiber optic cables are widely used in a variety of telecommunications applications, such as for long distance telephone networks spanning large geographic areas. A typical loose-buffered fiber optic cable for such an application includes a plurality of optical fibers contained within a cable core, in turn, protected by an overall jacket. The fibers may be maintained in identifiable groups by respective binder yarns within a centrally located single plastic buffer tube, or groups of fibers may be carded by a series of buffer tubes surrounding a central supporting member. Fiber optic cables may also include a plurality of tight-buffered fibers also collectively protected by an overall protective jacket.
One type of fiber optic cable includes a metallic shield surrounding the cable core. The metallic shield may be provided for rodent protection in a direct buffed or underground cable installation. An outer plastic jacket surrounds the metallic shield. It is also common in such a cable to incorporate lengthwise extending strength members within the cable jacket. For example, one version of an LXE.RTM. Lightguide Cable manufactured by AT&T includes a central loose-buffer tube, a surrounding corrugated metallic shield, and a pair of spaced apart metallic wires extending lengthwise along opposite sides of the o metallic shield.
The metallic components within a fiber optic cable are typically electrically grounded at predetermined points along the cable route, such as at splicing and termination points. This protects from electrical currents induced by power system disturbances, that is, nearby faults or from lightning induced surges.
The ends of fiber optic cables, and hence the electrical bonding assemblies for the metallic cable components, are typically housed within a protective splice closure. The splice closure is typically sealed to prevent the ingress of water into the splice closure which could o damage the optical fibers and/or splices. Such splice closures are disclosed, for example, in U.S. Pat. No. 5,121,458 entitled Preterminated Fiber Optic Cable to Nilsson, et al., U.S. Pat. No. 4,961,623 entitled Preterminated Optical Cable to Midkiff, et al., and U.S. Pat. No. 4,805,979 entitled Fiber Optic Cable Splice Closure to Bossard, et al.
A conventional bonding clamp for a telephone cable including multiple pairs of insulated copper conductors surrounded by an overall aluminum shield is disclosed in U.S. Pat. No. 4,895,525 entitled Cable Shield Grounding Clamp Connector to Leonardo. The bonding clamp includes a shoe plate or base member inserted between o the core of copper pairs and the surrounding metallic shield. The shoe plate has a threaded stud extending upwardly therefrom and scraping projections, extending upwardly along the opposite lengthwise edges of the shoe. A bonding plate having an opening therein receives the stud of the shoe and the bonding plate is positioned to overlie the outer protective jacket of the cable. The shoe and the bonding plate of the clamp have different radii of curvature so that they are biased apart. This conventional copper telephone cable bonding clamp, however, is undesirable for fiber optic applications where the cable includes o strength members.
U.S. Pat. No. 4,927,227 entitled Optical Fiber Cable Closure to Bensel, III, et al., and assigned to AT&T discloses a fiber optic splice closure including an electrical bonding clamp (the "AT&T clamp") for the metallic components within a fiber optic cable. The AT&T clamp includes a shoe plate having a threaded stud extending radially outwardly therefrom. The shoe is inserted between the cable core and the metallic shield of the cable. A first L-shaped member is secured with a portion overlying the shoe and on the opposite side of the metallic shield to thereby clamp the shield between the shoe and the first L-shaped member. A second L-shaped member is secured to the vertically extending portion of the first L-shaped member. A bonding block is secured to the vertically extending portions of the first and second L-shaped members so that the lengthwise extending strength members may be bent to extend in a radially outward direction from the cable and, thus, clamped between the bonding block and the second L-shaped member. The bonding block includes a pair of openings and associated set screws to secure a ground wire to the clamp to establish an electrical connection thereto.
Conventional fiber optic bonding damps, such as the AT&T clamp, may unfortunately permit relative movement between the strength members and the cable jacket so that water may migrate from the end of the cable and into the splice closure. Accordingly, such a bonding clamp is desirably partitioned off into a separate compartment within the splice closure to prevent water from entering into the splice area as shown in U.S. Pat. No. 4,927,227. The compartment is also filled with a water blocking compound.
When more than one conventional bonding clamp such as the AT&T clamp is used in a partitioned splice closure, all of the damps are connected to a common ground surrounded by the water blocking compound. Accordingly, the common electrical connection inhibits locating individual fiber optic cables in an underground installation, since signals cannot be separately introduced to the metallic shields of individual fiber optic cables.
The orientation of the strength members extending radially outward from the AT&T clamp precludes securing the strength members within the closure for additional support of the cable. The AT&T clamp is also relatively large compared to the cable and may prohibit installation of the clamp prior to insertion of the cable end into an opening in the end cap of the splice closure.